The only sane definition of "build-recommends" would be that the build
won't fail without these packages installed. Your example of texinfo
would most certainly cause the build to fail if it could not be found.

First, I never used an example of texinfo. I used an example of cdbs
and springgraph.

When backporting, we like to think people doing so have what we call
"intelligence" and are able to solve build problems, such as missing
deps, themselves.

When administering systems, we like to think people doing so have what
we call "intelligence" and are able to solve installation problems,
such as missing deps, themselves.

Oh, wait, that's a violation of a "must" in policy. Perhaps its is part
of the job of a Distro to make life easier for people? Quite frankly,
why should it take manual intervention to build packages? Just to make
life difficult?

Actually squat is a pure python package, it doesn't use anything from
build-essential and can be built easily without them installed.

LOL.

Actually, it does --- make. debian/rules is a makefile. I'm sure it
also uses dpkg-dev.

Yes it does, it just happens to include a binary distribution of itself
in its own source distribution.

"If necessary it will bootstrap the Ant code. Bootstrapping involves
the manual compilation of enough Ant code to be able to run Ant. The
bootstrapped Ant is used for the remainder of the build steps."